The police said the man was initially arrested on suspicion of attempted murder, but he was later charged with the “commission, preparation or instigation of terrorism including murder and attempted murder.”
“At this stage in the investigation, it is believed that the suspect acted alone but we are of course investigating all the circumstances leading up to the attack,” the force said in a statement.
Officers were searching a residential address in the Cardiff area, after the suspect injured 11 people in the attack on Muslims who had just left late-night prayers.
A man who died in the incident, after his legs were trapped under the van, had been sitting on the pavement while he was receiving first aid before the attack, police said.
The van used in the attack was reportedly hired in Wales.
Additional police were deployed near mosques in London and other cities following the attack.
Metropolitan Police Commissioner Cressida Dick said “people in the Muslim community, attending prayers, will see their police protecting them in coming days.”
Speaking alongside Dick in Finsbury Park, London mayor Sadiq Khan said police officers would be called back from leave to boost numbers in areas with large Muslim communities.
“Londoners will see more officers in their communities, particularly at and around mosques and places of worship, as Londoners observe Ramadan,” Khan said in a later statement.
“This is an extremely difficult time for our city, but I urge all Londoners to remain calm and vigilant.”
Prime Minister Theresa May and opposition leader Jeremy Corbyn made separate visits to Finsbury Park Mosque, close to the site of the attack.
“The terrible terrorist attack which took place last night was an evil born out of hatred and it has devastated a community,” May told reporters as she left the mosque.
“I am pleased to have been here today to see the strength of that community coming together, all faiths united in one desire to see extremism and hatred of all sorts driven out of our society,” she said.
Mohammed Kozbar, the chairman of the mosque, condemned the “cowardly attack which is no different than the [terrorist] attacks in Manchester and London.”
“Our community is in shock, our thoughts and prayer with those who have been effected by this,” Kozbar said in a statement on Facebook.
Witnesses described how the van veered off the road into a crowd of people leaving the area following late-night prayers.
After the suspect jumped out of the van, he shouted “I wanna kill all Muslims,” the BBC quoted witness Khalid Amin as saying.
Condemning the attack, the Muslim Council of Britain had called for security at mosques to be increased.
“It appears from eyewitness accounts that the perpetrator was motivated by Islamophobia,” the council’s secretary general Harun Khan said in a statement.
The council also clarified that the incident took place outside the Muslim Welfare House, 300 metres away from the mosque.
Video footage showed injured people lying on the ground and angry crowds surrounding a man believed to be the driver, according to The Independent.
An imam told British media he had protected the suspect from the crowd until police arrived to arrest him.
The suspect “was very quickly and calmly given over to the police,” Metropolitan Police Deputy Assistant Commissioner Neil Basu said, as he praised the community for their bravery.